Ordinarily, the combination of a first vehicle such as a motor home and a second vehicle such as an automobile or a light truck, where the first vehicle is towing the second vehicle, is stable on the road. However, there are circumstances when the combination can become unstable because of driving conditions normally encountered at highway speeds. For example, when the combination is overtaken by a large vehicle, it may be subject to wind turbulence effects of varying severity, depending on the size and speed of the overtaking vehicle. This can cause rocking, snaking or jackknifing of the combination. Such instabilities are known to cause accidents, particularly at highway speeds.
As another example, instabilities can arise as a result of the towing vehicle having to brake suddenly. In the case of sudden braking, the brakes of the towing vehicle are usually not designed to stop with the additional weight carried by the towed vehicle, resulting in a longer stopping distance than would otherwise obtain at normal towing vehicle weight. Moreover, the towed vehicle may decelerate more slowly than the towing vehicle, resulting in snaking, jackknifing or other instabilities.
As still another example, instabilities can arise as the result of the towing vehicle swerving to avoid road obstacles such as animals or tire debris. Ordinarily, if given sufficient time, the driver can avoid the obstacle by steering smoothly around it. However, if the obstacle is encountered suddenly, such as in circumstances where an animal darts out in front of the towing vehicle or the animate or inanimate obstacle is encountered on a curve or on a hill, the driver may attempt to avoid the obstacle by swerving suddenly and the combination may become unstable because the forward momentum of the towed vehicle may briefly cause the rear of the towing vehicle to skid in a sideways direction relative to the forward direction of the towing vehicle. Such instabilities manifest themselves as jackknifing or snaking and in severe cases, may result in the combination rolling over.
One method of returning an unstable combination to stability in situ is to accelerate the towing vehicle, causing a pull between the towing vehicle and the towed vehicle, which acts to dampen the instability. However, under certain circumstances, for example, if the combination is traveling down hill or if the speed of the combination is high at the onset of the instability or if jackknifing has caused the towing vehicle to swerve away from its intended direction, acceleration of the towing vehicle will not produce the required pull between the towing vehicle and the towed vehicle. Under such circumstances, acceleration of the towing vehicle can merely aggravate the situation.
In order to enable the combination of vehicles to slow safely or to decelerate the forward motion of the towed vehicle in a coordinated fashion with that of the towing vehicle, such as when the combination must swerve to avoid a road obstacle, several methods of applying the brakes of the towed vehicle have been developed. For example, in U.S. Pat. No. 2,177,469, White discloses an auxiliary hydraulic actuator for applying the brake pedal of the towed vehicle when the brakes of the towing vehicle are applied. The system does not require modification of the existing brake system of the towed vehicle. However, the vacuum required to operate the hydraulic pedal pusher is supplied by the vacuum system of the towing vehicle through a hose connecting the two vehicles. This approach requires costly connecting hoses and fittings. Moreover, an encounter with road debris could result in breakage or disconnection of the vacuum hose, resulting in a loss of vacuum in the engine of the towing vehicle and a shutdown of the power assist portion of the braking system without warning.
Another means of solving this problem was disclosed by Latham in U.S. Pat. No. 5,954,164. This patent teaches an inertial actuator for a towed vehicle braking system in which a weight, mounted on a pendulum, actuates the brake pedal of the towed vehicle. To augment the power assist function of the towed vehicle, an auxiliary vacuum system is provided. The installation of the inertial actuator module requires considerable time and effort. For example, the module is bolted to the floor of the towed vehicle, which may require drilling through the floor. In addition, a special fixture is required on the arm supporting the brake pedal for engagement with the pedal engaging surface. Installation of this fixture also requires holes to be drilled in the pedal arm. Considerable time must be spent dismounting the actuator module once the combination arrives at its destination.